“Situational interest” is a short-term form of motivation which occurs when a specific situation stimulates the focused attention of students (e.g., a spectacular science demonstration could arouse transient interest amongst nearly all the students in a class, even those who are not normally interested in science). However, there have been very few studies of situational interest and its potential to motivate students in science classrooms. The purpose of this project was to investigate situational interest and its sources. Small groups of grade 9 students participated in a science lesson which focused on inquiry skills, and data were obtained on their interest levels and sources of interest. The results indicated that interest arousal was substantial but did fluctuate throughout the lesson, according to the types of activities in which students were involved. The main source of interest was novelty, although choice, physical activity, and social involvement were also implicated.